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Chapter 4

ARH312Y1 Chapter Notes - Chapter 4: Younger Dryas, Microsoft Excel, Boundary Ranges

Course Code
Dr. A. Patton

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Impact of Climate Change During the Younger Dryas
This lab will investigate climate change and the idea that changes in climate during the
Younger Dryas influenced the development of food production. Using carbon dates obtained

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Climate Change and the Younger Dryas 2
from numerous site dates from Levantine Epipalaeolithic and Early Neolithic assemblages, this
paper will investigate the relationship between settlement patterns (including increased mobility
and cereal harvesting) in relation to climate deterioration during the Younger Dryas (12,900 cal
BP ±120).
The hypothesis that some of the changes in material culture and settlement patterns that
are associated with the Late Natufian (including increased mobility and cereal harvesting) could
have been “triggered” by the cold and dry conditions of the Younger Dryas.
BCal Software, Uncalibrated Radiocarbon Dates (from Maher et al. 2011)
Using the BCal Bayesian interface software, uncalibrated radiocarbon dates were
manually entered into the system. The data was separated into 4 groups that reflected the time
period (Pre-Pottery Neolithic A, Late Natufian, Early Natufian, Geometric Kebaran). The four
groups were then organized in relation to one another in a proposed model (in situ position) and
calibrated. Boundary parameters and confidence interval graphs were produced to analyze the
radiocarbon dates.
Probable Beginning and End dates1
Question 1)
The Model used for the radiocarbon date calibration was overlapping layers with late
overlap between Pre-pottery A and the early and late Natufian periods, and between the late and

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Climate Change and the Younger Dryas 3
early Natufian. Early overlapping layers were assumed between the early Natufian, Pre-Pottery
Neolithic A and the Geometric Kabaran. Overlap was used as an assumption of the sequence due
to the radiocarbon dates that were provided, there was overlap with the other time periods.
The ‘Ain Mallaha site has a C14 date of 460 BP (Maher et al. 2011) which appears to be
an extreme outlier. When my data was calibrated using the BCal software, there was a complete
overlap between the pre-pottery Neolithic A dates and the Late Natufian dates. Upon further
inspection, a box plot revealed multiple outliers in the data which have been identified before re-
calibration. Since time period boundaries are the values of interest, groups were organized
according to the time period ranges provided (Pre-pottery Neolithic A, Late Natufian, Early
Natufian, Geometric Kebaran).
To calculate and summarize the probably beginning and end dates, using the Bcal
software, HPD (High Posterior Density) regions estimates were generated. Since many of the
date ranges provided by the BCal software to reflect the early and late boundaries of each time
period had multiple range interval variations provided (some with large variation between one
another), A detailed step by step analysis and averaging if the CBal generated ranges (for the
68% confidence interval) is preformed for each boundary parameter for each chronological
period(Pre-pottery Neolithic A, Late Natufian, Early Natufian, Geometric Kebaran) due to the
different range intervals provided by the BCal software. The final calibrated dates for the upper
and lower boundaries for each time period is summarized in figure 16 located on page.18 of this
Figure 1: Diagram of overlap model used for calibration Figure 1: Diagram of overlap assumption using
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